1. Field of the Invention
The present invention relates generally to electronic circuits, and more particularly, to a digital-to-analog converter (DAC) for high frequency and/or high resolution environments.
2. Description of Related Art
In general, a digital-to-analog converter (DAC) converts a digital signal representing data bits to an analog signal. The DAC can converts bits in any electronics system such as a processing device. In high frequency applications and high resolution environments, conventional DACs have many shortcomings.
A thermometer DAC contains a dedicated cell for each bit received during a cycle. The cells are similarly sized. Thus, when a transition occurs between cycles each cell draws the same amount of energy from a voltage source. However, for high resolution applications, thermometer DACs require a large area of chip space. For example, a 12-bit thermometer DAC includes 4,095 cells to represent each possible combination.
Another alternative, a binary DAC, contains fewer cells than the thermometer DAC. Neighboring cells have a binary relationship, such as 1, 2, 4, and 8. Each cell has a different size, depending on the value it represents. One main problem with the binary DACs is the integrity of the output signal when input code changes by one step and a large cell (e.g. 8x) is turned on and all previous smaller cells (e.g., 1x+2x+4x=7×) are turned off. From low frequency point of view, due to mismatch the strength of the larger cell turned on may not be just one step larger than all previous cells summed up, therefore causing non-uniform steps or sometimes even negative step (non-monotonic). From a dynamic point of view, even if there is no DC mismatch, if the turn on and off time of the cells are not well synchronized, output signal can have glitches.
Therefore, what is needed is a DAC and method for data conversion suited to operate in high resolution and/or high frequency environments.